Preparation of aliphatic acids



U it State Patemofl 2,874,187 PREPARATION OF ALIPHATIC ACIDS No Drawing. Application December 27, 1956 Serial No. 630,758

Claims. (Cl. 260540) This invention relates to the preparation of propionic acid by hydrogenating o-cre sol.

The present application is a continuation-in-part of application'Serial No. 489,017, filed February 18, 1955 now Patent No; 2,786,873, issued March 26, 1957. The entire disclosure of the parent application is hereby incorporated. by reference. a t

At the present time, there is a need for additional sources of propionic acid since this material has become of increasing commercial importance.

It is a primary object of the present invention to prepare'propionic acid by a novel and economical reaction procedure.

Anloth'er objectiis to prepare propionic acid from ortho creso A further object is to simultaneously prepare propionic acid and phenol.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

It has now surprisingly. been found that if ortho cresol in the form of an alkaline salt is reacted with a hydrogen donor at an elevated temperature and pressure, there can be. obtained propionic acid in good yields. At the same time, significant yields of phenol are obtained. Thus, twoi commercially valuable products are simul taneously formed from a relatively inexpensive starting material.

The process is preferably carried out employing the sodium or other alkaline salt of o-cresol together with hydrogen at elevated temperature and pressure. In place of hydrogen, there can be employed hydrogen donors, such as the cycloaliphatic hydrocarbons, e. g., Tetralin, Decalin, cyclohexane, methyl cyclohexane, cyclopentane, 1,2 dimet hyl cyclohexane, ethyl cyclohexane, lithium hydride, sodium hydride, potassium borohydride, etc.

In place of individual o-cresol, there can be employed mixtures of phenols, such as cresylic acid or the phenolic fraction of coal tar boiling in the range of 150 to 250 C., or evenhigher.

The combined dealkylation and propionic acid formation is normally carried out at an elevated temperature which is usually between 350 and 550 C. More preferably, the temperature range is between 400 and 500 C.

Initial hydrogen pressure is usually between about 7 and 150 atmospheres with a preferred range between about and 75 atmospheres. Usually, the maximum pressure and final pressure during the hydrogenation both will be within the range of 7 to 150 atmospheres. It is to be understood that hydrogen pressures outside the indicated ranges can be employed, although such is not preferred operation. 7

2,874,187 Patented Feb. 17, 1959 A preferred source of hydrogen is coke oven gas.

The propionic acid, can be recovered as such or in the formof a salt such as sodium propionate, potassium propionate, ammonium propionate, barium propionate, calcium propionate, etc. i The hydrogen pressure is somewhat dependent upon temperature; in general, the higher the temperature of reaction, the higher the required pressure for satisfactory results. I

The alkali preferably shouldbe added in excess of the o-cresol. In general, ratios of alkalito phenolic hydroxyl groups on an equivalent basis (e. g., mols of sodium hydroxide to mols of cresol) of 350% of theory to of theory being preferred. As much as 440% or 460% or even more alkali can be added. Normally, there is no advantage in using a larger amount of alkali and,-in fact, the proportion of the o-cresol which reacts is reduced if the alkali is used in too large an excess. The use of a smaller amount of alkali than about 1.1 equivalent per phenolic hydroxyl group results in some dehydroxylation andlowering of yields of the desired propionic acid and phenol.

To some extent, the ratio of alkali to o.-cresol which is preferred depends on the other components of the neutralized charge. ,The phenols in the starting mixture can be neutralized with alkaline materials, preferably, the alkali metal hydroxides,v e. g., sodium hydroxide and potassium hydroxide or the corresponding carbonates, e. g., sodium carbonate or alkaline earth oxides or hydroxides, e. g., barium hydroxide, calcium oxide and calcium hydroxide. The use of calcium hydroxide is especially desirable if aromatic hydrocarbons, e. g., either or both of the isomericxm'ethyl naphthalenes are present. The amount of aromatic hydrocarbon can be between 0 and 10 parts per part of phenolic constituent in the original' mixture. p 7

Contact times between aboutone to 30 minutes, or even one or more hours, may be used, the time of contact varying to some extent, depending on the temperature employed as well as on the design of the equipment.

In carrying out the process of the present invention, ortho cresol, cresylic. acid or other o-cresol containing 'materialgwith or without admixture of aromatic hydrocarbons, is mixed with the required excess of alkali and the neutralized or alkaline mixture is then brought to a uniformly fused melt with substantial elimination .of free moisture. The uniform melt can be obtained either by careful heating with theaid of an agitator or by mixing with a large amount of previously fused melt at a high temperature. The fused or molten charge thus obtained .is then subjectedto hydrogen pressure in a closed reaction zone under conditions of gas liquid contact. This can be done in abateh or, more preferably, in a continuous process by the use of appropriate apparatus. After a period of reaction, which will depend onthe feed stock, hydrogen pressure and temperature, the pressure is released and the converted liquid material is separated from vthe hydrogen containing gases.

To aid in'the separation, some cooling can be pro vided eithe'rprior to the point of gas-liquid separation or to the gases leaving the primary separation zone. The hydrogen containing gases can be recycled in part to the reaction zone, the "-bleed being replaced by the corresponding quantity of fresh hydrogen gas, or the gases may be discarded or purified. Frequently, it is desirable to scrub the purge gas stream with a hydrocarbon oil to remove ethane and other lower hydrocarbons by-dissolving them in the oil. The remaining gas will then be enriched in hydrogen and, upon adding additional hydrogen, can be returned to the reaction zone.

The converted liquid products Whichcontain the salts of the propionic acid, phenol (hydroxybenzene) and any p. s. i.

unreacted or only partially dealkylated phenols can be.

sprung with an excess of an acidic material, e. g., sulfuric acid, hydrochloric acid, carbon dioxide, or sulfur dioxide. The acidic material added should be a stronger acid than the propionic acid and phenol. These materials can be added in the form of an aqueous solution or in anhydrous condition. Gaseous materials, such as hydrogen chloride and sulfur dioxide, for example, can be bubbled into the cooled mixture. Such methods of converting a phenolate, for example, to the free phenol are conventional in the art. After reaction with an acid, the product is distilled to separate propionic acid and pure phenol. Unconverted alkyl phenols are also separated by distillation and can be-recycled to the reaction zone. Some by-product material, such as meta cresol, can be retained for sale or for use as such, or it can be recycled for conversion into phenol.

As is evident from the above, although the reactant melt may be anhydrous, it is not essential that it be so. The initial formation of the melt is facilitated by the presence of some water.

In the present specification and claims, all parts are by weight unless otherwise specified.

The invention can be carried out continuously or by a batchwise process by mixing the o-cresol with alkali, heating to melt the mixture and then subjecting the fused charge to hydrogen pressure in a closed vessel, simultaneously cooling and releasing the pressure and separating the converted liquid material from the hydrogen containing gases. The liquid material is then further cooled, neutralized with acid and the liberated propionic acid and phenol separated and further purified in conventional manner.

In the following examples, all pressures are gauge pressures.

Example I 18 parts of ortho cresol were melted and mixed in a vessel with 7.5 parts of sodium hydroxide with agitation. The temperature of the mixture was raised to 400 C. and hydrogen gas introduced at an initial pressure of 510 p. s. i. The reaction was allowed to continue for minutes. During that time, the pressure reached a maximum of 1050 and a final pressure of 450 p. s. i. resulted. The liquid was separated from the gases, cooled and then 35 parts of sulfuric acid of 25% concentration were added. The oils were extracted with excess ether and the ether then evaporated. The oil was then fractionally distilled to separate the propionic acid in a first portion and phenol as a second higher boiling fraction.

The neutralized product included 2.4 parts of phenol (15% based on the cresol charged) and 7.8 parts of o-cresol as well as substantial amounts of propionic acid. There were no sodium hydroxide insolubles in the product.

Example II The procedure of Example I was repeated, using a reaction temperature of 450 C. The maximum pressure developed was 1200 p. s. i., and the final pressure at room temperature was 450 p. s. i., as in Example I. The neutralized product contained 4.1 parts of phenol (26% yield), 3.5 parts of o-cresol, substantial amounts of propionic acid and 2.0 parts of sodium hydroxide insolubles.

Example III 18 parts of o-cresol were melted and mixed in a vessel with 15 parts of sodium hydroxide with agitation. The temperature of the mixture was raised to 450 C. and hydrogen gas introduced at an initial pressure of 510 The reaction was allowed to continue for 15 minutes. During that time, the pressure reached a maximum of 1460 p. s. i. and a final pressure of 690 p. s. i. resulted. The liquid mixture was separated from the gases, cooled and then 70 parts of sulfuric acid of 25% concentration were added. The propionic acid and phenols were recovered from the neutralized mixture in conventional manner, as in Example I. The recovered product included 4.1 parts of phenol (26% yield), 5.6 parts o-cresol, no sodium hydroxide insolubles, substantial amounts of propionic acid and 0.85 part of methane.

Example IV Example III was repeated, using a reaction time of 45 minutes. The pressure reached a maximum of 1100 p. s. i. and the final pressure was 550 p. s. i. The final product included 5.9 parts of phenol (37% yield), considerable propionic acid, 7.4 parts of o-cresol and no sodium hydroxide insolubles.

Example V Example III was repeated, using 30 parts of sodium hydroxide and a reaction time of 45 minutes. The maximum pressure developed was 1660 p. s. i. and the final pressure was 790 p. s. i. 150 parts of hydrochloric acid of 20% concentration were used to liberate the free phenols. The final product included 4.3 parts of phenol (27% yield, but a 93% yield, based on the o-cresol which reacted), propionic acid, 12.7 parts o-cresol and no sodium hydroxide insolubles.

' Example VI Example IV was repeated, using an initial hydrogen pressure of 250 p. s. i. The maximum pressure developed was 1200 p. s. i. and the final pressure was 565 p. s. i. The product contained 5.3 parts of phenol (34% yield), considerable propionic acid, 8.4 parts of o-cresol, 1.3 parts of methane and no sodium hydroxide insolubles.

Example VII 21 parts of a cresylic acid containing 92% phenolic constituents and 8% alkylated hydrocarbons, principally, alpha and beta methyl naphthalenes, were melted and mixed with 18 parts of calcium oxide with agitation. The temperature of the mixture was raised to 460 C. and simultaneously, hydrogen gas introduced at an initial pressure of 500 p. s. i. The reaction was allowed to continue for 45 minutes. During that time, the pressure reached a maximum of 1600 p. s. i. and a final pressure of 650 p. s. i. resulted. The liquid mixture was separated from the gases, the aromatic hydrocarbons removed by steam stripping and the liquid mixture cooled and then parts of hydrochloric acid of 20% concentration were added. The phenols and propionic acid were recovered from the neutralized mixture in conventional manner using a fractional distillation, as in Example I. The recovered product included 10.8 parts of phenol, 5.1 parts of the alkylated phenols in the original cresylic acid, 1.1 parts of naphthalene and 0.2 part of the methyl naphthalenes present in the original cresylic acid, as well as propionic acid.

Example VIII 36 g. (0.33 mol) of o-cresol, 30 g. (0.75 mol) of NaOH and 11.1 g. of Tetralin (used as a hydrogen donor) were heated in a 250 ml. Magnedash autoclave to 450 C. and held there for one hour. The pressure reached 1020 p. s. i. and on cooling to 25 C. was 400 p. s. i. The material was removed from the autoclave and dissolved in water. The Tetralin which was not soluble in water was removed. The aqueous solution was made acid with H SO and the oils extracted with ether and the ether evaporated. The oil was analyzed by infra-red and distilled. The cut boiling around C. (l18175 C. cut) was identified as propionic acid by several methods.

Yields in mol percent were as follows:

Recovered 0.19 mol or 57 mol percent o-cresol unchanged, 0.52 mol or 16 mol percent phenol, 0.65 mol or 20 mol percent propionic acid.

There were also 6 g. loss as to vapor and 1.9 g. of high boiling material.

Example IX Hydrogen was used instead of Tetralin, as in Example VIII. 18 g. o-cresol and 30 g. of NaOH were added to a 250 ml. autoclave and pressured to 500 p. s. i. with hydrogen, heated to 450 C. and held one hour. The pressure reached 1700 p. s. i. and the final pressure on cooling was 790 p. s. i. at 25 C. In this case 37 mol percent o-cresol was recovered and 20% phenol. in the range of 120 C. was found which contained propionic acid.

It is believed that butadiene is also formed as a result of the cracking.

We claim:

1. A process for the preparation of propionic acid comprising contacting an alkaline mixture of ortho cresol and an alkali with a hydrogen donor selected from the group consisting of hydrogen, Tetralin, Decalin, cyclohexane, methyl cyclohexane, cyclopentane, 1,2 dimethyl cyclohexane, ethyl cyclohexane, lithium hydride, sodium hydride, and potassium borohydride at elevated temperature and pressure and thereafter acidifying the mixture and recovering the propionic acid by distillation.

2. A process according to claim 1 wherein the hydrogen donor is hydrogen.

3. A process according to claim 1 wherein the reaction is carried out at a pressure between about 7 and 150 atmospheres.

A cut boiling 4. A process according to claim 3 wherein the reaction is carried out at a temperature between about 350 C. and about 550 C.

5. A process according to claim 1 wherein the alkali is an alkali metal hydroxide.

6. A process according to claim 5 wherein the alkali is sodium hydroxide.

7. A process according to claim 1 wherein an excess of alkali is present in the reaction so that the equivalent ratio of alkali to ortho cresol is in the range of between about l.1-to 1.0 and about 4.6 to 1.0.

8. A process according to claim 7 wherein the alkali is sodium hydroxide.

9. A process for the preparation of propionic acid comprising contacting an alkaline mixture of ortho cresol and an alkali with hydrogen at elevated temperature and pressure, removing the hydrogen, acidifying the mixture with acid and recovering the propionic acid formed from the phenol formed and from the residual cresol by fractional distillation.

10. A process according to claim 9 wherein the alkali is sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 2,786,873 Ohsol et a1 Mar. 26, 1957 

1. A PROCESS FOR THE PREPARATION OF PROPIONIC ACID COMPRISING CONTACTING AN ALKALINE MIXTURE OF ORTHO CRESOL AND AN ALKALI WITH A HYDROGEN DONOR SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, TETRALIN, DECALIN, CYCLOHEXANE, METHYL CYLOHEXANE, CYCLOPENTANE, 1,2 DIMETHYL CYCLOHEXANE, ETHYL CYCLOHEXANE, LITHIUM HYDRODE, SODIUM HYDRIDE, AND POTASSIUM BOROHYDRIDE AT ELEVATED TEMPERATURE AND PRESSURE AND THEREAFTER ACIDIFYING THE MIXTURE AND RECOVERING THE PROPIONIC ACID BY DISTILLATION. 